1. Field of the Invention
The present invention relates to a process for producing 2-butanone and 2-butanol by directly oxidizing n-butane using molecular oxygen.
2 Background Art
2-Butanone is conventionally produced by synthesizing 2-butanol and dehydrogenating the resulting 2-butanol. As a process for producing 2-butanol used as the raw material, hydration of 1-butene or 2-butene which is a lower olefin is known.
As the hydration process of the butenes, an indirect hydration process in which sulfuric acid is added to the double bond of an olefin and the resulting product is subjected to hydrolysis, and a direct hydration process in which the double bond of an olefin is subjected to hydration using a catalyst as disclosed in Japanese Patent Publication No. 62-61573 and the like are known.
However, the indirect hydration process using sulfuric acid gives rise to problems such as an increase in the number of steps consisting of sulfuric acid absorption, sulfonation, hydrolysis, and separation/concentration, corrosion of a reactor due to acids, and disposal of waste sulfuric acid and waste water.
The direct hydration process of butenes does not use sulfuric acid. However, this process requires a high reaction temperature of 120-180xc2x0 C. and a high pressure of 40-200 bars. Moreover, use of steam for hydration may cause water to be mixed into the reaction system.
Accordingly, an object of the present invention is to produce 2-butanone and 2-butanol under comparatively mild conditions with a decreased number of steps by directly oxidizing a raw material hydrocarbon, which is cheaper than butenes, using molecular oxygen such as air.
As a result of extensive studies to attain the above object, the present inventors have found that 2-butanone and 2-butanol can be obtained at a lower temperature and a lower pressure with a decreased number of steps by directly oxidizing n-butane or a hydrocarbon mixture containing n-butane, which is cheap and conventionally used as a fuel, as the raw material using molecular oxygen in the presence of a specific catalyst. This finding has led to the completion of the present invention.
Specifically, the present invention provides a process for producing 2-butanone and 2-butanol comprising directly oxidizing n-butane using molecular oxygen in the presence of aluminum phosphate containing transition metal atoms.
In the production process of the present invention, a selectivity improving agent may be allowed to be present in combination.
In the production process of the present invention, n-butane or a hydrocarbon containing n-butane is used as the raw material. As the hydrocarbon containing n-butane, a butane-butene fraction, produced from a petrochemical unit as a by-product, or a residual fraction obtained by removing butenes from the butane-butene fraction are suitably used. Butenes and the like may remain in these fractions used as the raw material. However, if the n-butane content is too small, the ratio of by-products increases. Therefore, the n-butane content in these fractions is preferably 60 weight % or more, and particularly preferably 80 weight % or more.
As molecular oxygen used for oxidization, high-purity oxygen gas or air, mixed gas in which high-purity oxygen gas or air is diluted with nitrogen, helium, argon, methane, or the like may be used.
Aluminum phosphate containing transition metal atoms used in the process of the present invention acts as a catalyst component. This aluminum phosphate consists of an aluminum atom, phosphorus atom, and oxygen atom as essential components, or further contains a silicon atom or magnesium atom in combination with these atoms. The aluminum phosphate containing an aluminum atom, phosphorus atom, and oxygen atom as the essential components is shown by AlPO-m (m is an integer showing a crystalline type), wherein the ratio of aluminum atoms, phosphorus atoms, and oxygen atoms is approximately 1:1:4. The aluminum phosphate containing a silicon atom or magnesium atom in combination with an aluminum atom, phosphorus atom, and oxygen atom is shown by SAlPO-n or MAlPO-n (n is an integer showing a crystalline type), in which part of the aluminum atoms is replaced by a silicon atom or magnesium atom. The ratio of the sum of aluminum atoms and silicon atoms or magnesium atoms, phosphorus atoms, and oxygen atoms is approximately 1:1:4.
In the process of the present invention, the aluminum phosphate containing transition metal atoms used as the catalyst component is a compound in which part of the aluminum atoms of the above aluminum phosphate is replaced by one or more types of transition metal atoms. This means that transition metal atoms are not merely bonded to the aluminum phosphate physically.
There are no specific limitations to the transition metal atoms replacing the aluminum atom in the aluminum phosphate insofar as its valence change due to electron transfer during oxidation-reduction is one or more. Therefore, copper, titanium, vanadium, iron, cobalt, manganese, chromium, and the like can be given as examples of such transition metals. Of these, vanadium, manganese, cobalt, and copper are particularly preferable.
The amount of transition metal atoms included in the aluminum phosphate is determined so that the percentage of the amount of transition metal atoms in the total amount of transition metal atoms and aluminum atoms is 0.01-20 mol %, and preferably 0.01-10 mol %. If the amount of transition metal atoms exceeds the upper limit, heat stability or crystallinity of the catalyst may decrease. If the amount of transition metal atoms is less than the lower limit, sufficient catalytic activities may not be obtained.
The aluminum phosphate containing transition metal atoms is porous, which is a kind of molecular sieve. This aluminum phosphate has a crystal structure ranging from nearly amorphous to crystalline. The aluminum phosphate, which has any type of the above crystal structures may be used as the catalyst. Of these, porous crystalline aluminum phosphate with a pore diameter of 3-10 angstroms is preferable from the viewpoint of catalytic activities, selectivity of the objective product, and heat stability of the catalyst.
In the production process of the present invention, the amount of the aluminum phosphate containing transition metal atoms used as the catalyst is 0.01-10 weight %, and preferably 0.02-1 weight % of n-butane used as the raw material.
In the present invention, oxidization may be carried out using a batch-type or continuous-type liquid phase process. As the type of reactor, any of a bubble tower-type, stirring-type, circulation-type, and stirring/circulation-type may be employed. The reaction temperature is 50-150xc2x0 C., and preferably 80-130xc2x0 C. If the temperature is less than the lower limit, sufficient activities ay not be obtained. If the temperature exceeds the upper limit, the amount of by-products such as butenes, acetaldehyde, acetic acid, acetone, and carbon dioxide or the amount of decomposition products increases. The reaction pressure is from atmospheric pressure to 10 MPa, and preferably 0.5-5 MPa.
In the process of the present invention, a selectivity improving agent may be added to the reaction system in order to improve selectivity. As the selectivity improving agent, water, pyridine, fluorinated hydrocarbons, hydrogen peroxide, and organic peroxides are preferable. Of these, water, pyridine, hydrogen peroxide, and fluorinated hydrocarbons such as perfluorooctane are particularly preferable. These selectivity improving agents are added in an amount based on weight from {fraction (1/100)} to 50 times, and preferably from {fraction (1/10)} to 30 times the amount of the aluminum phosphate containing transition metal atoms.
In the process of the present invention, a mixture of 2-butanone and 2-butanol is obtained from n-butane. The mixture is separated by distillation to obtain a product. 2-Butanol in the resulting mixture may be converted into 2-butanone by dehydrogenation using a dehydrogenation catalyst to obtain a product. 2-Butanone thus obtained is useful as a high performance solvent in various fields such as paint and adhesives. 2-Butanol is useful as a solvent, a raw material for producing 2-butanone, and the like.